This application is based on Japanese Patent Application Nos. 11-160154 (1999) filed Jun. 7, 1999 and 2000-159934 (2000) filed May 30, 2000, the contents of which are incorporated hereinto by reference.
The present invention relates to an ink jet printing apparatus, and in particular, to a technique for detecting a failure in ejection from an ink jet print head and detecting adhesion of an ink to a face of the ink jet print head on which ejection openings are formed.
Ink jet printing apparatuses based on the ink jet printing method, one of non-impact printing methods, can perform high-density and high-speed printing with low noise, by ejecting inks from ejection openings to print images on printing media such as paper, cloths, plastic sheets, or OHP sheets (hereafter also simply referred to as xe2x80x9crecording paperxe2x80x9d). The ink jet printing method is very excellent and has a simple configuration, but has problems.
That is, since ink jet printing apparatuses directly eject inks onto the printing medium through the fine ejection openings to form images, ejection may fail when a print head face with the ejection openings formed therein (hereafter referred to as an xe2x80x9cejection facexe2x80x9d) is wet with the inks. There are two main causes of the wetting. First, the inks ejected for printing may strike on the printing medium and partly bounce off without adhering thereto, or upon ink ejection, in addition to the inks principally involved in printing, fine ink droplets may be ejected and float in the atmosphere. These inks or fine ink droplets may adhere to the ejection face.
An ejection failure may also occur during a recovery operation for preventing the ejection openings from being clogged or for removing the clog, that is, when a cap is placed on the ejection face and removed therefrom after sucking the ink from nozzles. In this case, ink resulting from this processing may remain on the ejection face. This is because the sucking operation causes the cap to be filled with the ink, so that when the cap has been removed from the ejection face, the ink in contact with the ejection face remains there. To prevent this, the ejection face may be subjected to liquid repulsion treatment, but this method still has difficulties in completely eliminating the remaining ink.
In addition, in order to remove the ink remaining in the cap when the cap is removed from the ejection face after the sucking through the ejection openings, a thin-plate-shaped absorbent made of a porous resin or a nonwoven cloth is installed in the cap. Without the absorbent, if the sucking operation is performed while the cap is open in order to eliminate the ink therefrom, only the ink immediately close to a drain opening in the cap is sucked, while the ink surrounding the opening remains. That is, the absorbent allows a negative pressure or sucking pressure to act gently, thereby causing the ink to be uniformly sucked from the cap.
If such the undesired inks adhere to neighborhoods of the ejection openings, an inappropriate ejection may occur, including a xe2x80x9cbiasxe2x80x9d wherein the ink ejection direction deviates from a normal one or an xe2x80x9cejection failurexe2x80x9d wherein the ink cannot be ejected, the print quality lowers in result. Since particularly strict quality control is required in using the ink jet printing apparatus for industrial purposes as a textile printing or a printing machine, such degradation is a critical problem associated with the reliability of the apparatus.
To solve this problem, a method is often employed which wipes the ejection face using a blade (which may also be referred to as a xe2x80x9cwipersxe2x80x9d) composed of an elastic member such as rubber (this method is hereafter referred to as xe2x80x9cwipingxe2x80x9d). To achieve the wiping, the print head is scanned by the stationary blade to wipe the ejection face, or while the print head is stationary, the blade is translated or rotated to come in contact with the ejection face.
In the above described conventional examples, however, if the wiping is insufficient for any reason (this is hereafter referred to as xe2x80x9cinappropriate wiping), part of the ink fails to be wiped, resulting in an inappropriate ejection.
It is an object of the present invention to promptly and reliably detect an ejection state of an ink jet print head without affecting actual print operation sequences.
It is another object of the present invention to detect adhesion of an ink to an ejection face during an inappropriate ejection detecting operation, thereby effectively preventing inappropriate ejection arising from inappropriate wiping.
Generally, the present invention comprises a light emitting section for emitting a light beam in a direction diagonally traversing an arrangement direction of nozzles and a light receiving section used for detecting whether an ink droplet or an ink adhered on an ejection face is passed in the light beam.
In a first aspect of the present invention, there is provided an ink jet printing apparatus for carrying out printing by moving an ink jet head in a scanning direction relatively to a printing medium, the ink jet head having a plurality of ejection openings arranged therein for ejecting an ink, the apparatus comprising:
means for emitting a light beam in a direction which is different from the arrangement direction of the plurality of the ejection openings and which traverses a trace of the ink ejected through the ejection openings;
means for receiving the emitted light beam;
means for controlling the light emitting means to emit the light beam and for controlling the ink jet head to eject ink through the plurality of the ejection openings in accordance with predetermined data, while the ink jet head is being relatively moved in the scanning direction between the light emitting means and the light receiving means; and
means for detecting ink ejection states from the plurality of the ejection openings based on light beam receiving states at the light receiving means.
Here, the light emitting means and the light receiving means may be provided along the scanning direction of the ink jet head and outside a print area.
In a second aspect of the present invention, there is provided a judgement method of an ink ejection state of an ink jet head for carrying out printing by moving in a scanning direction relatively to a printing medium, the ink jet head having a plurality of ejection openings arranged therein for ejecting an ink, the method comprising the steps of:
controlling light emitting means to emit a light beam in a direction which is different from the arrangement direction of the plurality of the ejection openings and which traverses a trace of the ink ejected through the ejection openings and controlling the ink jet head to eject ink through the plurality of the ejection openings in accordance with predetermined data, while the ink jet head is being relatively moved in the scanning direction; and
detecting ink ejection states from the plurality of the ejection openings based on blocking states of the light beam.
The first or second aspect of the present invention may comprise means for, or a step of judging adhesion of the ink to a face of the ink jet head on which the plurality of the ejection openings are formed, based on the detection by the detecting means or step.
When the judgement means judges that the ink adheres to the face, the face may be wiped after the detection means or step has completed a series of detection sequences for the plurality of the ejection openings.
Moreover, the judgement means or step may determine whether that ejection opening for which a normal ejection has not been detected during the detection sequences carried out by the detection means or step for the plurality of the ejection openings is identical and/or close to that for which the normal ejection was not detected during the previous detection sequence, and wherein if the result of the determination is affirmative, the judgement means or step may judge that the ink adheres to the face.
Here, means for or step of storing information of the ejection opening for which the normal ejection has not been detected during each of the detection sequences carried out by the detection means or step for the plurality of the ejection openings may be comprised, and wherein the judgement means or step makes the determination based on the stored information.
On judging that the ink adheres to the face, the judgement means or step may allow to store this judgement.
In the above, the ink jet head may have heating elements for generating thermal energy to make the ink to film-boil, as an energy used for ejecting the ink.
Incidentally, hereafter, the term xe2x80x9cprintxe2x80x9d (hereinafter, referred to as xe2x80x9crecordxe2x80x9d also) represents not only forming of significant information, such as characters, graphic image or the like but also represents to form image, patterns and the like on the printing medium irrespective of whether it is significant or not and whether the formed image elicited to be visually perceptible or not, in broad sense, and further includes the case where the medium is processed.
In addition, the term xe2x80x9cprinting mediumxe2x80x9d refers to paper for use in general printing apparatuses as well as a medium such as a cloth, a plastic film, and a metallic plate and the like and any substance which can receive inks ejected by the heads in a broad sense.
Further, the term xe2x80x9cinkxe2x80x9d has to be understood in a broad sense similarly to the definition of xe2x80x9cprintxe2x80x9d and should include any liquid to be used for formation of image patterns and the like or for processing of the printing medium.
Additionally, the term xe2x80x9cnozzlexe2x80x9d, as used hereafter, collectively refers to an ejection opening, a liquid passages in communication therewith, and an element for generating energy for use in ink ejection, unless otherwise specified.
In addition, the term xe2x80x9cejection failurexe2x80x9d refers to an actual failure to eject the ink from the nozzle and a failure to appropriately eject a predetermined amount of ink in a predetermined direction, that is, an inappropriate ejection.